a) Field of the Invention
This invention relates to bicycle cranks for pedal driven bicycles and specifically to a means to allow the bicycle crank a predetermined amount of elasticity that can be controlled and measured as a rider of the bicycle imparts force to the crank pedals.
b) Description of the Related Art
U.S. Pat. No. 5,257,540 (Bower et al, issued Nov. 2, 1993; the present inventor is a co-inventor in this patent) teaches an ingenious bicycle crank, whereby the crank relies on the introduction of an elastic support structure between a) the axle, on the ends of which the pedal assemblies are mounted and b) the chain ring assembly. (The chain ring assembly refers to one or more annular disks of different sizes forming a rigid assembly, each disc having circumferential teeth). When pedal force is applied, the elastic member allows an angular deflection between the chain ring assembly and the axle. The elastic support structure is composed of an annular disc having radial slots therein or a solid anisotropic material, oriented such that the elasticity is greater in the circumferential direction. The elasticity is not adjustable in the prior art.
The elastic bicycle crank provides at least three structures that together form a functional unit. The first structure incorporates an axle having two pedal cranks attached to either end of the axle. The second structure is a chainring assembly comprising one or more annular discs that form a rigid assembly having a rigid set of teeth. Each disc has teeth on its periphery for engaging a drive chain. The above two structures are well known in the art. The third structure elastically connects the chainring assembly to the axle to allow for deflection therebetween. The previous patent, referenced herein, describes this elastic member as being formed from a disk having radial slots to provide some elasticity. Although this construction is quite effective in providing, in that patent, the best mode of operation with a workable and ingenious solution to the invention, the new elastic member structure provides adjustable deflections by connecting the chainring assembly structure and the axle structure with an adjustable U-shaped spring assembly. This U-shaped spring assembly allows for constant, but readily adjustable, elasticity. Having an adjustable elastic structure allows different bicycle riders an increased benefit of adjustable sensitivity. Each bicycle rider may set the amount of elasticity and the sensitivity to his or her needs. In particular, each rider may set the degree of elasticity to the proper amount to allow accurate calibration of associated measurement instrumentation which may indicate the rider""s pedal force and other important data.
A primary object of this invention is to provide an elastic bicycle crank that is simple in operation and will provide a repeatable amount of deflection given a defined amount of pedal force. Another object of this invention is to provide an elastic member that is adjustable. A further object of the invention is to allow ease of assembly of the elastic member. Yet another object is to have the spring assembly replaceable with springs of different diameters, external shapes, and cross-sectional areas. An additional object of the invention is to allow for mechanical stops that will prevent damage to the elastic member if placed under a force that would exceed the normal limits of operation. These and other objects will be apparent to those skilled in the art from the following detailed description of a preferred embodiment of the invention.